Apparatus of controlling tracking for a disk

ABSTRACT

The present invention relates to an apparatus of measuring how much an eccentricity affects each phase of a disk and controlling disk tracking based on the each effect rate. The present apparatus with disk phase identifying means stores information on dense/sparse state of a tracking error (TE) signal in connection with characteristic of an output signal from said means while a tracking servo is inactivated, and, in data reproduction mode, it identifies a current disk phase based on characteristic of the output signal from said means, and adjusts tracking characteristic of the tracking servo based on the stored information in connection with signal characteristic in order to compensate effect rate of eccentricity on the identified disk phase. Through minute adjustment of servo characteristic for each disk phase, error range of TE signal to track in real time is reduced, whereby, tracking for an eccentric disk becomes easier and more reliable.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a tracking control apparatus fora disk recording medium, more particularly, to an apparatus of measuringhow much an eccentricity affects each phase of a disk and controllingdisk tracking based on the measured each effect rate.

[0003] 2. Description of the Related Art

[0004] In general, most of the disks become eccentric during rotationbecause of variation in disk manufacturing or disk clamping condition.If an eccentricity of a disk is too high to conduct an exact tracking,it is difficult to reproduce data from the disk normally.

[0005] To overcome such a bad situation, a disk device measures aneccentricity of a disk and adjusts characteristic of a tracking servo tocompensate the measured eccentricity at a start-up operation.

[0006] A conventional eccentricity measuring method rotates a placeddisk with a tracking servo off, counts pulse train produced every trackcross of an optical pickup and disk revolutions, and divides the pulsecount by the number of disk revolutions. Because the value resulted fromthe division represents how much a disk is eccentric, gains of atracking servo are adjusted based on the eccentricity measured as aboveto compensate eccentricity of the disk overall.

[0007] However, even though eccentricity of a disk is high, the higheccentricity has different effects on respective disk phases. Namely, acertain disk phase is affected less by the high eccentricity than otherphases.

[0008] Nevertheless, if gains of a tracking servo are increased to makemore sensitive to compensate an eccentricity overall irrespective ofdifferent effect of eccentricity on respective disk phases, a trackingservo may diverge unexpectedly, namely, an objective lens of an opticalpickup may be biased to the utmost side when a scratch is encountered ona disk phase an eccentricity has small effect on.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a disktracking control apparatus that measures how much an eccentricity of arotating disk affects respective disk phases and that adjustscharacteristic of a tracking servo minutely according to the measuredindividual effect on each disk phase.

[0010] A disk device of reproducing data from a disk recording medium inaccordance with the present invention is characterized in that itcomprises: reading means reading signals written on a rotating recordingmedium and producing recorded signals and a tracking error signal out ofthe read signals; a phase encoder generating a signal of whichcharacteristic varies according to phase of the rotating disk; a servounit controlling tracking of an objective lens equipped in said readingmeans; and a controller storing information on dense/sparse state of thetracking error signal in connection with characteristic of the signalgenerated by said phase encoder while tracking servo of said servo unitis inactivated, and, in data reproduction mode, identifying a currentdisk phase based on characteristic of the signal generated by said phaseencoder, and adjusting tracking characteristic of said servo unit basedon the stored information in connection with the signal characteristicin order to compensate an effect rate of eccentricity on the identifieddisk phase.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are included to provide afurther understanding of the invention, illustrate the preferredembodiments of the invention, and together with the description, serveto explain the principles of the present invention.

[0012] In the drawings:

[0013]FIG. 1 is a simplified block diagram of a disk device in which thefirst embodiment of a disk tracking control method of the presentinvention is embedded;

[0014]FIG. 2 illustrates a trajectory of an optical pickup on aneccentric disk;

[0015]FIG. 3 shows an illustrative TE signal produced from a diskrotating eccentrically in the tracking-off state and a pulse train ofwhich duty ratios are different;

[0016]FIG. 4 shows an information table where effect rates ofeccentricity on respective disk phases are written in connection withcorresponding disk phases in accordance with the first embodiment of thepresent invention;

[0017]FIG. 5 is a simplified block diagram of a disk device in which thesecond embodiment of a disk tracking control method of the presentinvention is embedded;

[0018]FIG. 6a shows an arrangement of a phase encoder shown in FIG. 5with respect to a placed disk;

[0019]FIG. 6b is a plane view of a disk with a phase identifiabletransparent circle-band structured in accordance with the secondembodiment of the present invention;

[0020]FIG. 6c illustrates data of which 1's (or 0's) ratio varies inaccordance with disk phrase in the second embodiment of the presentinvention; and

[0021]FIG. 6d shows an exemplary information table where effect rates ofeccentricity on respective disk phases are written in connection withcorresponding disk phases in accordance with the second embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] In order that the invention may be fully understood, a preferredembodiment thereof will now be described with reference to theaccompanying drawings.

[0023]FIG. 1 is a simplified block diagram of a disk device in which thefirst embodiment of a disk tracking control method of the presentinvention is embedded.

[0024] The disk device of FIG. 1 comprises an optical pickup 20 forreading written signals from the surface of an optical disk 10; an R/Funit 30 for producing binarized signals and a TE (Tracking Error) and aFE (Focusing Error) signal through filtering and combining the signalsdetected by the pickup 20; a driving unit 50 for driving a sled motor 21to move the optical pickup 20 and a spindle motor 22 to rotate the disk10; a servo unit 40 for conducting tracking/focusing operation of anobjective lens in the pickup 20 and controlling the driving unit 50 torotate the disk 10 at a constant speed; a digital signal processing unit60 for restoring original data from the binarized signals using a selfclock synchronized with the binarized signals in phase; a phase encoder80 for generating a pulse train with duty ratio varying cyclicallyduring rotation of the spindle motor 22; a memory 90 for storing data;and a microcomputer 100 for controlling an overall reproducingoperation, especially, for measuring eccentricity effect on each diskphase based on the pulses from the phase encoder 80 and adjustingtracking servo characteristic of the servo unit 40 according to measuredindividual eccentricity effect.

[0025] When the disk 10 is placed on a tray (not shown) equipped in thedisk device, the microcomputer 100 controls the driving unit 50 throughthe servo unit 40 to rotate the placed disk 10 in CLV (Constant LinearVelocity) manner by the spindle motor 22. While the disk 10 is rotated,the phase encoder 80 outputs successive pulses that have different dutyratios cyclically, e.g., pulses 302 with increasing duty ratio as shownin FIG. 3. The pulses are applied to the microcomputer 100. The phaseencoder 80 may be implemented with an FG signal generator that isintegrated in the spindle motor 22 in general.

[0026] The microcomputer 100 controls the servo unit 40 to turn afocusing servo on and a tracking servo off. This state with focusing onand tracking off is called ‘traverse state’.

[0027] If the disk 10 is little eccentric during rotation, an objectivelens of the optical pickup 20 would form an ideal trajectory 201 on thedisk 10 in traverse state as illustrated in FIG. 2, otherwise, it wouldform an undesirable trajectory 202.

[0028] Therefore, TE signal would be produced like as 301 of FIG. 3 incase of an eccentric disk. For example, if the trajectory 202 of FIG. 2is partitioned into four phases, sinusoidal TE signal is dense at phases‘a-b’ and ‘c-d’ and sparse ‘b-c’ and ‘d-a’.

[0029] The waveform 301 of TE signal drawn, in FIG. 3 is produced onlywhen tracking servo is off. Namely, TE signal is not produced like asFIG. 3 in case that tracking servo is activated to record/reproduce datafrom a disk.

[0030] The microcomputer 100 samples the TE signal, and pulses from thephase encoder 80 simultaneously and stores sampled data in the memory90.

[0031] After the disk 10 rotates at least once, the microcomputer 100analyses the sampled data in the memory 80. Through the analysis, themicrocomputer 100 identifies dense and sparse section of the TE signaland examines ranges of duty ratio of the pulses for respective dense andsparse sections at the same time. In the analysis, if values ofsuccessive sampled data show rapid change it is dense section and if dosmooth change it is sparse section. As another way, a section havingrelatively more peak values is judged dense and the other section issparse.

[0032] In addition, the microcomputer 100 counts the number of peakvalues (or vibrations) for respective dense and sparse sections tomeasure effect rate of eccentricity on each section. Each count isstored in connection with corresponding section. Finally, a desirableinformation table is constructed in the memory 90 as illustrated in FIG.4. Each turning point from dense to sparse and vice verse is determinedto a boundary between dense and sparse section.

[0033] After construction of the information table like as FIG. 4, ifdisk reproduction is requested the microcomputer 100 moves the pickup 20to an initial or a target position in order to reproduce data from thedisk 10. At the same time, the microcomputer 100 calculates duty ratioof pulses outputted from the phase encoder 80.

[0034] And, the microcomputer 100 identifies which range among thestored variation of duty ratio in the memory 90 the calculated dutyratio belongs to. For example, if the calculated duty ratio is about40%, the microcomputer 100 judges a current disk phase to ‘a-b’referring to the information table of FIG. 4.

[0035] Because the information table shows that the disk phase ‘a-b’ isbadly affected by disk eccentricity, possibility of tracking error isrelatively high in this disk phase. Thus, the microcomputer 100increases gains of the tracking servo or an amplifying rate of the TEsignal in proportion to effect rate at the detected disk phase ‘a-b’.Consequently, the tracking servo becomes so sensitive that it can trackbetter even in a bad disk phase where a track swings severely.

[0036] If the calculated duty ration is about 60%, the current phase isdetermined to ‘b-c’ where effect rate of eccentricity is relatively low.Thus, the microcomputer 100 makes the tracking servo insensitive.Because of insensitiveness of the tracking servo, the tracking servo isless likely to diverge even though unexpected noise of TE signal arisesin the disk phase of low effect-rate of eccentricity.

[0037] In addition, because the microcomputer 100 is able to know howmuch a next track following current one on the identified disk phase isaffected by disk eccentricity, it can adjust characteristic of thetracking servo to meet a next track in advance before the next trackarrives. For example, if the calculated duty ratio is about 50%, whichmeans that the current phase is ‘a-b’, it can be known that a next diskphase (phase ‘b-c’) is less affected by disk eccentricity. Therefore,the microcomputer 100 may make the tracking servo of presenthigh-sensitivity insensitive before the pickup 20 reaches the phase‘b-c’. If characteristic of the tracking servo is adjusted beforehand,tracking servo operates with low sensitivity as soon as a track on thephase ‘b-c’ is reproduced.

[0038]FIG. 5 is another simplified block diagram of a disk device inwhich the second embodiment of a disk tracking control method of thepresent invention is embedded. The disk device shown in FIG. 5 replacesthe phase encoder 80 encoding rotation angle of the spindle motor 22with a phase encoder 110 encoding phase directly from a placed disk. Theother elements are same as the disk device of FIG. 1.

[0039] The phase encoder 110 of FIG. 5, as shown in FIG. 6a, includes alight emitting unit (LEU) 17 radiating a planar beam arranged radiallywith respect to a placed disk onto the disk; and a light detecting unit(LDU) 18 that is composed of a series of photo diodes or phototransistors detecting the planar beam individually.

[0040] The LEU 17 may be implemented with a series of laser diodesarranged in a line or with a single light emitting element and anenclosing box of which bottom has parallel slits that transform a lightfrom the light emitting element into parallel individual beams.

[0041] Furthermore, a disk 11 for this embodiment has a phaseidentifying circle-band 11 a along outermost circle 102 as shown in FIG.6b. The phase identifying circle-band 11 a includes a transparent innercircle-band 11 c of which width varies linearly from 0 at a certainstart line 11 b to full width of the phase identifying band 11 a at thatline 11 b.

[0042] The phase encoder 110 is placed to cover above and below thephase identifying circle-band 11 a of the disk 11 as shown in FIG. 6a.

[0043] A microcomputer 120 included in the disk device of FIG. 5 has asmany input ports as the outputs of the phase encoder 110 as shown inFIG. 5. Namely, each input port of the microcomputer 120 is connected toan output pin of each photo diode or photo transistor.

[0044] While the disk 11 structured as above is rotated in the diskdevice of FIG. 5, the parallel beams 171 from the LEU 17 of the phaseencoder 110 are incident to the LDU 18 at the opposite side only throughthe transparent inner circle-band 11 c formed in the phase identifyingcircle-band 11 a. Therefore, the microcomputer 120 receives n-bit datasequentially in the form of FIG. 6c through its input ports while thedisk 11 rotates.

[0045] The microcomputer 120 identifies a current disk phase based onthe ratio of ones (or zeros) to n bits inputted from the phase encoder110.

[0046] Afterwards, the microcomputer 120 measures disk eccentricitybased on vibration of TE signal and effect rate of eccentricity on eachof partitioned disk phases in the traverse state the same as in thefirst embodiment. The measured quantities are stored in the memory 90.FIG. 6d shows an exemplary information table including the measuredquantities.

[0047] During data reproduction (or record), a current disk phase isidentified from the ratio of ones (or zeros), to n-bit data outputtedsimultaneously from the phase encoder 110, and effect rate ofeccentricity on the identified disk phase is known from the informationtable stored in FIG. 6d. Finally, characteristic of the tracking servois adjusted accordingly to meet the known effect rate of eccentricity onthat phase. This shortly-explained operation is totally same with thefirst embodiment explained in detail before.

[0048] The above-explained disk tracking control method adjusts servocharacteristic for each disk phase to match with different effect rateof eccentricity on each disk phase. Thus, an error range of TE signal totrack in real time is reduced, whereby, tracking for an eccentric diskbecomes easier and more reliable.

[0049] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A disk device of reading data from a diskrecording medium, comprising: reading means reading signals-written on arotating recording medium and producing recorded signals and a trackingerror signal out of the read signals; a phase encoder generating asignal of which characteristic varies according to phase of the rotatingdisk; a servo unit controlling tracking of an objective lens equipped insaid reading means; and a controller storing information on dense/sparsestate of the tracking error signal in connection with characteristic ofthe signal generated by said phase encoder while tracking servo of saidservo unit is inactivated, and, in data reproduction mode, identifying acurrent disk phase based on characteristic of the signal generated bysaid phase encoder, and adjusting tracking characteristic of said servounit based on the stored information in connection with the signalcharacteristic in order to compensate an effect rate of eccentricity onthe identified disk phase.
 2. The disk device of claim 1, wherein thesignal characteristic is duty ratio.
 3. The disk device of claim 2,wherein said phase encoder is integrated to a motor rotating therecording medium.
 4. The disk device of claim 1, wherein the signalcharacteristic is the ratio of ones or zeros to parallel bits.
 5. Thedisk device of claim 4, wherein said phase encoder is composed of alight emitting unit radiating parallel beams and a light detecting unitreceiving the parallel beams, both units being installed in radialdirection above and below an outermost circumference of the recordingmedium.
 6. The disk device of claim 4, wherein said phase encoderoutputs parallel bits where the ratio of ones or zeros varies accordingto what portion of parallel beams passes through a transparentcircle-band formed along an outermost circumference of the recordingmedium, the transparent circle-band varying linearly in width.
 7. Thedisk device of claim 1, wherein said controller adjusts the trackingcharacteristic of said servo unit to sensitive if the signalcharacteristic stored in connection with the identified disk phase showsdense.
 8. The disk device of claim 1, wherein said controller adjuststhe tracking characteristic of said servo unit to insensitive if thesignal characteristic stored in connection with the identified diskphase shows sparse.
 9. The disk device of claim 1, wherein saidcontroller checks effect rate of eccentricity on a next phase to theidentified disk phase, and adjusts the tracking characteristic of saidservo unit in advance before the next phase arrives.
 10. The disk deviceof claim 1, wherein said controller adjusts the tracking sensitivity ofsaid servo unit in proportion to the number of sinusoidal waves of thetracking error signal that is stored in connections with the identifieddisk phase.
 11. The disk device of claim 1, wherein said controllerconsiders the recording medium to be partitioned into four phases.